The prion diseases are characterized by aggregation of a mis-folded isoform of the prion protein, termed PrP (Sc). No treatment is available to halt progression of prion diseases, and as such, clinically viable therapies are being sought. Potent pyridine-based compounds have been designed to mimic dominant negative PrP and hence bind to auxiliary molecules involved in the conformational conversion of PrP(C) to PrP (Sc). These compounds have been shown to inhibit PrP (Sc) replication and have been analogued using SAR techniques. While the EC(50)s of the original lead compounds were in the 15-30 micromolar range, the most potent new analogues are active at 300 nanomolar concentrations. Independently, we have identified the acridine-based compound, quinacrine as a potent anti-prion agent in a cell-based assay of PrP(Sc) replication (EC(50)=300 nanomolar), and developed bis-quinacrine analogs that are even more potent (EC(50)=30 nanomolar). Given the improved activity of the bis- analogs, subsequent research efforts will focus on developing this class of compound. Refinement of bioactive pyridine- and bis-acridine-based analogs using synthetic libraries and computational methods could furnish potent non-toxic heterocyclic compounds that could be viable candidates for the treatment of prion disease. The cellular and molecular mechanism of action of the pyridine- and acridine-based compounds is being examined to better understand how these compounds reduce PrP(Sc) replication in a cell-based model of prion disease. The trafficking of PrP(C) and PrP(Sc) between cellular compartments will be determined using a neuronal imaging system employing confocal microscopy. Subsequently, fluorophore labeled pyridine- and acridine-based analogs will be introduced to the imaging system to determine if these compounds exert their effect on PrP(Sc) replication by interfering with the trafficking of the prion protein. Photoactivatable labeled analogs will be synthesized for receptor cross-linking studies. These probes will be used to identify the molecular targets of the heterocyclic-based compounds. Once the molecular targets have been isolated and characterized, the structural and functional information pertaining to the targets will be used for the structure-based design of potent and selective compounds, active against PrP(Sc) replication.